1. Field of the Invention
The present invention relates to a semi-automatic welding unit capable of simultaneously completing multiple welds, for use in low to medium volume spot welding applications.
2. Description of the Prior Art
Automotive assembly processes have generally focused on large volume mass production techniques. Such production volumes, which may exceed 60 units per hour, require fully-automated, high-speed assembly equipment which is capital intensive and, due to time constraints inherent in such production, must be duplicated for each operation, since movement of these units is impractical during assembly and production. Such high capital expenditures are, however, justifiable in view of the correspondingly high production volumes and also in view of the displacement of manual labor operations which, in many industrialized markets, are costly relative to markets with low labor costs.
Welding is a process which typically falls into the above category. As an automobile body progresses along a high-volume assembly line, various welding operations are generally performed by individual welding units which are each responsible for a single, or relatively low number of operations at a localized position on the vehicle. For example, on a typical four-door sedan having two hinges per door, up to eight welding units must be employed to join the hinges to the door pillars.
Renewed interest in low volume models of a specialty type has seen production rates for some models dipping as low as 12 to 15 units per hour. This decrease in production, combined with a proliferation of models from various markets, has inevitably required new assembly processes. Additionally, the removal of significant production to developing nations with relatively low labor costs, requires development of production processes which utilize this inexpensive labor efficiently. The present invention addresses the above problems in its application to welding units.